About a week ago I was planning a ported box for two 12s. They called for 2 cubes each, so the box was upwards of 4 cubes. While doable, I decided it would take up too much trunk space, so I went back to the drawing board and came up with a sealed design. My two RF Punch He2s call for 1.25 cubes each, or 2.5 together sealed. This design gives me that with room for sub displacement and fits perfectly in the back of the trunk of the '02 Elantra.

Here's the trunk to give you an idea of the space I'm trying to fill (the "cave" in the back):

And here's my color-coded cardboard mockup of the planned enclosure. The top will be sealed shut, it's just hinged so you can see inside. There a couple places where it's a little short, but I reworked the design so everything will be flush in the end.